Except for fat men - we'll buy anything that makes us sound thinner.People, I mean men of course, don’t like anything labelled small and won’t buy them.
But back to bike frames, I'm about average height of around 5' 8", and my favoured frame size (old style steel) is 23". And watching eBay, that seems to be about the average size that I see. I see quite a few 25" frames, but also a lot of smaller ones.